1. Field of the Invention
The invention is in the field of electronic solid state device processing, more particularly, semiconductor wafer or metal thin film conductivity measurement.
2. Brief Description of the Prior Art
The ability to rapidly and accurately measure the electric conductivity of thin flat samples (lamellae) is of critical importance in many aspects of solid state device processing. Such measurements are essential parts of the classification of semiconductor substrate materials prior to processing, to the monitoring of dopant diffusions and the monitoring of metal thin film depositions. The most widely used measurement technique is the four point probe method. However this method has several limitations, for example, it is difficult to interpret the results of such a measurement made on high resistivity semiconductor samples. In addition the probe causes localized surface damage at the point of contact. Such surface damage becomes more and more detrimental as the element size of microminiature circuits becomes smaller.
Various noncontacting techniques for the measurement of electrical conductivity have been developed in an effort to avoid the limitations of the four point probe technique. These methods generally involve the interaction of the sample being measured with high frequency excitations. Exemplary techniques of this class include: microwave transmission measurements through a semiconductor slab placed in a waveguide (H. Jacobs et al. Proceedings of the IRE, 49 (1961) 928); reflection of an RF signal from a coaxial line terminated by the sample (C. A. Bryant et al. Reviews of Scientific Instruments, 26 (1965)1614); and capacitive coupling and inductive coupling to a resonant circuit (N. Nuyamoto et al. Reviews of Scientific Instruments, 38 (1967) 360; J. C. Brice et al. Journal of Scientific Instruments, 38 (1961) 307). Such methods typically produce nonlinear output signals which require calibration over the range of use and comparison of the measurement signals to the calibration curve. In addition, such measurements have typically made use of some relatively ill defined measurement volume (e.g., approximately hemispherical), which may be quite satisfactory for the measurement of uniformly conductive samples, however, increase the complexity of analysis of measurement results for nonuniform samples (e.g., diffused layers in semiconductors).